The present invention generally relates to a socket connector for connecting a circuit board and a processor. More particularly, certain embodiments of the present invention relate to flexible contacts that accommodate differing co-efficients of thermal expansion while remaining coplanar in a socket connector.
Many large electronic devices, such as computers, use socket connectors to connect different electronic components. For example, land grid array (LGA) socket connectors are used to electrically connect electronic packages, such as processors, to circuit boards. The conventional socket connector includes a frame surrounding a base. The base includes an array of holes therein that hold contacts in a pattern that corresponds to a pattern of electrical traces provided on the circuit board and contact pads provided on the bottom of the processor. The socket connector is mounted on the circuit board with the contacts engaging the electrical traces. The processor is then positioned on the base with the processor contact pads aligned and engaging the contacts to facilitate electrical communication between the processor and the circuit board.
The contacts are retained in vertical channels in the base of the socket connector. Each contact has a vertical support beam that is formed perpendicularly at a first end with a base beam carrying a solder ball. The support beam is also formed at an opposite second end at an obtuse angle with a contact beam. The support beam and the base beam are generally the same thickness, yet the support beam includes retention barbs that extend from opposite sides thereof. Each contact is inserted into a channel in the base with the retention barbs engaging channel walls to retain the contact within the channel. The contact beam extends out of the channel at an acute angle with respect to a top surface of the base. The base beam extends beyond a bottom surface of the base in a direction generally parallel to the base. The base beam suspends the solder ball under the base.
In operation, a socket cover is mounted to the socket connector. A tool is attached through a vacuum to a top surface of the socket cover and transports the socket cover and socket connector onto the circuit board with the solder balls resting on the electrical traces on the circuit board. The socket connector and socket cover are placed in a reflow soldering oven, which effectively solders the solder balls to the electrical traces on the circuit board. The socket cover is then removed and the processor is positioned on the socket connector with the contact pads engaging corresponding contact beams.
However, conventional socket connectors suffer from several drawbacks. First, the support beams on the contacts do not hold the base beams firmly against the bottom surface of the base. For example, the base beams are manufactured to be at right angles to the support beams and the channels are manufactured to be at right angles to the bottom surface. However, manufacturing tolerances cause the contact and the base to have an acute angle therebetween. Therefore, some of the base beams will extend beyond the bottom surface at a slight acute angle. Thus, the base beams and solder balls are not all coplanar along the bottom surface of the base. When the contacts and solder balls are not entirely coplanar, some of the solder joints between the contacts and the circuit board that are produced during reflow soldering are incomplete or even open. Improper solder joints result in a poor electrical connection between the processor and the circuit board.
Additionally, the rigid manner in which the support beam holds each contact in the corresponding channel prevents the contact from accommodating the effects of differing co-efficients of thermal expansion among the contact, base, and circuit board. For example, the contact may expand at a greater rate than the base and circuit board during temperature changes. Because the contact cannot axially flex within the channel to adjust for such expansion, the contact applies greater resistant forces on the base and the circuit board, which can lead to strains in the base and damaged connections at the solder joints.
Also, because the socket cover covers the contacts in the base, the socket cover blocks heat from reaching the solder balls during the reflow soldering process. Thus, the socket cover can cause poor or even open solder joints between the solder balls and the circuit board.
A need exists for a socket connector that addresses the above noted problems and others experienced heretofore.